1. Field of the Invention
The invention relates to additive combinations of an ethylene backbone type polymer and a second polymer having long linear alkyl side chains extending from ester groups, for improving the cold flow properties of low viscosity distillate fuel oil.
2. Prior Art
Various ethylene backbone polymers as pour point depressants for middle distillate fuel oil have been described in the patent literature. The more effective of these distillate oil pour depressants are copolymers of ethylene with various other monomers, e.g., copolymers of ethylene and vinyl esters of lower fatty acids such as vinyl acetate (U.S. Pat. 3,048,479); copolymers of ethylene and alkyl acrylate (Canadian Patent 676,875); terpolymers of ethylene with vinyl esters and alkyl fumarates (U.S. Pats. 3,304,261 and 3,341,309); polymers of ethylene with other lower olefins, or homopolymers of ethylene (British Patents 848,777 and 993,744); chlorinated polyethylene (Belgium Patent 707,371 and U.S. Pat. 3,337,313); etc.
In addition, various oil-soluble polymers characterized by long linear side chains extending from ester groups have recently become known as flow improvers for crude oils, residua-containing fuel oils, and in some cases, for distillate oils. One group of polymers described in British Patent 1,215,214 and U.S. Pat. 3,447,916 is prepared by condensation reactions of a dicarboxylic acid, or anhydride with a basic material which can be a polyol, polyamine or amino alcohol, together with a monocarboxylic acid. The resulting condensation polymer e.g., a polyester, is taught as a flow improver for residual and distillate fuel oils. A futher improvement of this type of flow improver condensation polymer is described in British Patent 1,215,214, wherein pentaerythritol is the polyol. Similarly, ester addition polymers having long linear side chains have been described in British Pats. 1,154,966, 1,161,188 and 1,197,474 as flow improvers for crude and residua-containing fuel oils. The most important of these addition polymers are prepared by polymerizing long chain unsaturated esters, such as copolymers of vinyl acetate and behenyl fumarate, or homopolymers of behenyl methacrylate, etc. Another class of addition polymers, which are taught as useful in residua are those described in South African Patent 70/6785, and published German Application 1,940,944. Here, long chain alpha olefins are copolymerized with maleic anhydride, which copolymer is then esterified with long straight chain alcohols.
More recently, synergistic combinations of various ethylene backbone pour point depressants with certain long chain ester polymers as flow improvers for residua containing fuels or distillates from flash distillation of residua, have been described in British Patent 1,300,227.